DNA methylation patterns in tumors derived from F9 cells resemble methylation at the blastula stage

We show here that the genome of F9 teratocarcinoma cells growing in culture is heavily methylated but undergoes massive demethylation in tumors derived by subcutaneous injection of the cells. This demethylation occurs primarily in single copy gene sequences. As a result imprinted genes acquire their characteristic monoallelic methylation patterns while non-imprinted genes undergo demethylation. The overall methylation pattern in the tumors resembles the pattern observed in the mouse preimplantation embryo. The F9 cells in the tumors apparently recognize imprinted genes, distinguish them from non-imprinted genes and change the methylation of both gene classes to the pattern which characterizes the embryo. These cells therefore have the potential of prodding an abundant source of protein factors involved in establishing the methylation pattern during embryo development.